Improved open circuit voltage in CuInS/sub 2/-based solar cells

Abstract

The conversion efficiency of thin film solar cells based on CuInS/sub 2/ (/spl eta/=12%) is mainly limited by a moderate open circuit voltage (/spl ap/720 mV). This limitation can be overcome by modifying the absorber/buffer interface leading to open circuit voltages exceeding 800 mV. The addition of ZnS to the CuInS/sub 2/ as well as adjusting the preparation conditions for the CdS-buffer leads to an increased V/sub oc/. The coevaporation of ZnS or CdS additives and diffusion from precursor layers for two types of fabrication processes has been examined: codeposition of the elements and diffusion of Cu and S into In/sub x/S/sub y/ layers. The addition of ZnS leads to Zn-rich segregations on the CuInS/sub 2/ surface. No shift of the bandgap due to the Zn incorporation could be measured. Additionally, an improved sulfur incorporation using the binary In/sub 2/S/sub 3/ as the In and S source was found.